Satellite observations of humid heat extremes over Africa

Background and Rationale
Humid heat is a serious risk to human health, reducing the body's ability to expel heat through sweating. The human impact of heat extremes will increase under climate change, particularly in tropical 'hot spots', such as equatorial Africa, which is highly populated, already very hot and humid and vulnerable to climate variability. Whilst there is a fairly well established body of research on dry bulb temperature extremes, there is very limited understanding of the meteorological drivers of humid heat extremes.
Emerging work suggests that humid heatwave formation is the result of a complex interaction between moist processes involving cloud, rainfall, evaporation and moisture advection (Birch et al. 2022), alongside a lack of mixing in the lower atmosphere, which prevents the ventilation of heat (Raymond et al. 2021). Humidity, rather than temperature, is the stronger driver of humid heat extremes in the arid regions of Africa, whereas both temperature and humidity are drivers in the already very humid equatorial tropics (Birch et al. 2022). There is a critical need to regionally assess the extent to which humid heat is modulated by atmospheric circulation, cloud, rainfall and surface fluxes and evaluate these drivers in climate models at the regional scale.
Climate and atmospheric science research is challenging over Africa due to a lack of routine and detailed observations over much of the continent. Studies must therefore rely on satellite retrievals, which have the advantage of providing regular coverage over the entire continent. For example, a previous study by satellite expert and PhD co-supervisor Dominique Bouniol used a range of spaceborne observational datasets to characterise the processes involved in the formation of a heatwave over the Sahel region of West Africa and found that cloud and moisture were increasing temperatures through the longwave greenhouse effect.
Climate projections are almost ubiquitously provided by relatively coarse resolution regional or global climate models, which are known to poorly represent the key moist processes that can cause or ventilate severe moist heat stress events. Over Africa, this translates into an underestimation of present day humid heatwave frequency, and their future change (Birch et al. 2022). Convective-scale (grid spacing <5km) regional climate models are run at a sufficiently high resolution to allow the convective parameterisation to be turned off and to represent the largest convective motions explicitly. Convective-scale models are thus better able to represent processes important for humid heat extremes such as intense rainfall and dry spells, the atmospheric water cycle and soil moisture-precipitation feedbacks. Convective-scale models provide an opportunity to advance process-based understanding of humid heat extremes, but have yet to be fully exploited in this way.
Aims and Objectives
The aim of the project is to characterise the drivers of African humid heat extremes and evaluate their representation in high-resolution climate models. This aim will be addressed through the following objectives:
Use satellite retrievals of the Earth's energy and radiative budgets, cloud, rainfall, temperature and water vapour to quantify the drivers and key characteristics of humid heat extremes over different regions of Africa for observed case studies and on average, over many past events.
Evaluate the representation of African humid heat extremes and in convective-scale and CMIP6 climate model simulations against satellite observations.
Use the pan-African convective-scale climate simulations, including any new ensemble simulations, to assess the uncertainty in future projections of humid heat extremes